Adding the Salesforce Connector by QuickBooks app is only available in QuickBooks Online Advanced US version, @it-vincihairclin.
I recognize how relevant it is to you and your business to automatically downloads your closed Salesforce opportunities and creates draft invoices from the data on the opportunities.
In the meantime, you'll want to consider using other third party application. Simply, proceed to the Apps menu in your QBO account or visit our QuickBooks Apps to check for an application that has same function as the Salesforce Connector by QuickBooks.
You can also check out this resource you can utilize for future task that will guide you in personalizing your sales forms: Customise invoices, estimates, and sales receipts in QuickBooks Online.
As always, input a comment below if you have any other questions about adding a Salesforce Connector by QuickBooks. I'm here to help always. Take care!